rtc: fix hrtimer deadlock

commit b830ac1d9a2262093bb0f3f6a2fd2a1c8278daf5 upstream.

Ben reported a lockup related to rtc. The lockup happens due to:

CPU0                                        CPU1

rtc_irq_set_state()			    __run_hrtimer()
  spin_lock_irqsave(&rtc->irq_task_lock)    rtc_handle_legacy_irq();
					      spin_lock(&rtc->irq_task_lock);
  hrtimer_cancel()
    while (callback_running);

So the running callback never finishes as it's blocked on
rtc->irq_task_lock.

Use hrtimer_try_to_cancel() instead and drop rtc->irq_task_lock while
waiting for the callback.  Fix this for both rtc_irq_set_state() and
rtc_irq_set_freq().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Ben Greear <greearb@candelatech.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Change-Id: I2b1a13e50b81eda763e175c58c7886e7c7b7f692
Reviewed-on: http://gerrit.lud.stericsson.com/gerrit/35594
Tested-by: Per VAHLNE <per.xx.vahlne@stericsson.com>
Reviewed-by: Jonas ABERG <jonas.aberg@stericsson.com>

0 files changed, 0 insertions, 0 deletions